CAST

Syntax

CAST(expr AS type)

Description

The CAST() function takes a value of one type and produces a value of another type, similar to CONVERT(). See the description of CONVERT() for more information.

The main difference between the CAST() and CONVERT() is that CONVERT(expr,type) is ODBC syntax while CAST(expr as type) and CONVERT(... USING ...) are SQL92 syntax.

MariaDB starting with 5.5.31

Until MariaDB 5.5.31, X'HHHH', the standard SQL syntax for binary string literals, erroneously worked in the same way as 0xHHHH. In 5.5.31 it was intentionally changed to behave as a string in all contexts (and never as a number).

This introduces an incompatibility with previous versions of MariaDB, and all versions of MySQL (see the example below).

Examples

Simple casts:

SELECT CAST("abc" as binary);
SELECT CAST("1" as unsigned integer);
SELECT CAST(123 as char character set utf8)

Note that when one casts to CHAR without specifying the character set, the collation_connection character set collation will be used. When used with CHAR CHARACTER SET, the default collation for that character set will be used.

SELECT collation(cast(123 as char));
+------------------------------+
| collation(cast(123 as char)) |
+------------------------------+
| latin1_swedish_ci            |
+------------------------------+

SELECT collation(cast(123 as char character set utf8));
+-------------------------------------------------+
| collation(cast(123 as char character set utf8)) |
+-------------------------------------------------+
| utf8_general_ci                                 |
+-------------------------------------------------+

If you also want to change the collation, you have to use the COLLATE operator:

SELECT collation(cast(123 as char character set utf8) collate utf8_unicode_ci);
+-------------------------------------------------------------------------+
| collation(cast(123 as char character set utf8) collate utf8_unicode_ci) |
+-------------------------------------------------------------------------+
| utf8_unicode_ci                                                         |
+-------------------------------------------------------------------------+

Using CAST() to order an ENUM field as a CHAR rather than the internal numerical value:

CREATE TABLE enum_list (enum_field enum('c','a','b'));

INSERT INTO enum_list (enum_field) VALUES('c'),('a'),('c'),('b');

SELECT * FROM enum_list ORDER BY enum_field;
+------------+
| enum_field |
+------------+
| c          |
| c          |
| a          |
| b          |
+------------+

SELECT * FROM enum_list ORDER BY CAST(enum_field AS CHAR);
+------------+
| enum_field |
+------------+
| a          |
| b          |
| c          |
| c          |
+------------+

From MariaDB 5.5.31, the following will trigger warnings, since x'aa' and 'X'aa' no longer behave as a number. Previously, and in all versions of MySQL, no warnings are triggered since they did erroneously behave as a number:

SELECT CAST(0xAA AS UNSIGNED), CAST(x'aa' AS UNSIGNED), CAST(X'aa' AS UNSIGNED);
+------------------------+-------------------------+-------------------------+
| CAST(0xAA AS UNSIGNED) | CAST(x'aa' AS UNSIGNED) | CAST(X'aa' AS UNSIGNED) |
+------------------------+-------------------------+-------------------------+
|                    170 |                       0 |                       0 |
+------------------------+-------------------------+-------------------------+
1 row in set, 2 warnings (0.00 sec)

Warning (Code 1292): Truncated incorrect INTEGER value: '\xAA'
Warning (Code 1292): Truncated incorrect INTEGER value: '\xAA'

See Also

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